Ab inito study and NBO analysis of the enantiomerization energy profile of tetra-peri-substituted overcrowded naphthalenes

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• 作者：Davood Nori-Shargh ; Maryam Malekhosseini and Farzad Deyhimi
• 关键词：Tetra-peri-substituted naphthalene ; Molecular modeling ; Chiral stability ; Ab initio
• 刊名：Journal of Molecular Structure: THEOCHEM
• 出版年：2006
• 出版时间：28 April 2006
• 年：2006
• 卷：763
• 期：1-3
• 页码：187-198
• 全文大小：483 K

文摘

Ab initio molecular orbital (MO) and density functional theory methods were used to investigate the structural and conformational properties of 1,4,5,8-tetra-tert-butyl naphthalene (1), 1,4,5,8-tetrakis(trimethylsilyl)naphthalene (2), 1,4,5,8-tetrakis(trimethylgermyl)naphthalene (3) and 1,4,5,8-tetrakis(trimethylstannyl)naphthalene (4). HF/3-21G*//HF/3-21G*, MP2/3-21G*//HF/3-21G*, B3LYP/3-21G*//HF/3-21G*, HF/LANL2DZ*//HF/LANL2DZ*, MP2/LANL2DZ*//HF/LANL2DZ* and B3LYP/LANL2DZ*//HF/LANL2DZ* results revealed that the most stable form of these compounds has D₂ symmetry, and, therefore, they should present optical activity. The enantiomerization processes for compounds 1–4 could take place via plane symmetrical intermediates (with C_2h symmetry). MP2/3-21G*//HF/3-21G* results show that the plane-symmetrical (C_2h symmetry) geometries of compounds 1–4 are less stable (about 8.40, 5.18, 8.01, and 6.37 kcal mol⁻¹, respectively) than the axial-symmetrical geometries (D₂ symmetry). Also, in compounds 1–4, the plane symmetrical intermediate (C_2h symmetry) is less stable than the axial-symmetrical (D₂ symmetry) geometry, about 10.07, 6.80, 9.49 and 7.33 kcal mol⁻¹, respectively, as calculated by B3LYP/3-21G*//HF/3-21G* level of theory. The barrier heights for interconversion of the D₂ to C_2h geometries for compounds 1–4 are 29.32, 14.89, 12.28 and 9.24 kcal mol⁻¹, as calculated by MP2/3-21G*//HF/3-21G* level of theory. Also, B3LYP/3-21G*//HF/3-21G* results show that the required energy for ring flipping (D₂ to ) for these compounds is 28.41, 13.48, 11.52, 8.33 kcal mol⁻¹. In both axial and plane symmetrical (D₂ and C_2h) geometries of compounds 1–4, the naphthalene rings are puckered and their aromatic characters are relatively perturbed.

For compounds 1–3, the calculations were also performed at B3LYP/6-311+G**//HF/6-31G*, MP2/6-31G*//HF/6-31G* and HF/6-31G*//HF/6-31G* levels of theory. However, the comparison showed that the results at HF/3-21G*//HF/3-21G*, B3LYP/3-21G*//HF/3-21G* and MP2/3-21G*//HF/3-21G* methods correlated well with those obtained at HF/6-31G*//HF/6-31G*, B3LYP/6-311+G**//HF/6-31G* and MP2/6-31G*//HF/6-31G* levels of theory.

Further, NBO analysis, based on the HF/3-21G* optimized ground state geometries, revealed that in compounds 1–4, the resonance energy associated with σ_Caryl–M to delocalization is 1.43, 3.53, 3.96 and 4.62 kcal mol⁻¹, respectively. These resonance energy values could explain the easiness of ring flipping processes from compound 4 to 1. The NBO results are in good agreement with the calculated energy barriers for ring flipping in compounds 1–4, as calculated by MP2, B3LYP and HF methods, using all electron (3-21G*) and pseudopotential (LANL2DZ*) basis sets.